Process for the production of conjugated poly-olefins



Patented July 27, 1943 UNITED STATES PATENT OFFICE PROCESS FOR THE PRODUCTION OF CONJUGATED POLY-OLEFINS George W. Hearne and George A. Stenmark,

Berkeley, Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application January 22, 1940,

Serial No. 315,076

Claims.

The present invention relates to isomerization or rearrangement, and more particularly pertains to the rearrangement of acetylenic hydrocarbons into compounds having at least two olefinic linkages in conjugated position with respect to each other. The invention specifically covers a novel process for the production of hythe invention covers a process for the rearrangement of dimethyl acetylene and/or ethyl acetylene to produce butadiene.

According to the present invention this rearrangement of the acetylinic hydrocarbons into poly-olefinic hydrocarbons having the double bonds-or olefinic linkages in conjugated relation to each other may be realized by subjecting the acetylenic hydrocarbons of the above-outlined and hereinbelow more fully described class, to elevated temperatures in the presence of a catalyst which has an alkaline reaction. As such, it is possible to use activated alumina.

As stated above, the invention covers the rearrangement or isomerization of hydrocarbons comprising or containing an aliphatic chain of at least four carbon atoms, this chain containing at least one acetylenic linkage the acetylenic carbon atoms of which are not attached to any tertiary carbon atom. These compounds include dimethyl acetylene, ethyl acetylene, methylethyl acetylene, methyl propyl acetylene, and the like, their homologues and analogues. phatic chain may contain more than one acetylenic linkage provided such chain contains a sufficient number of carbon atoms to permit the rearrangement to form poly-olefins in which the double bonds are in conjugated position or relation to each other. As examples of thistype of acetylenic hydrocarbons which may be isomerized in accordance with the present process, reference is made to octadiyne-2,6, decadiyne-2,8,- and the like. Also, the aliphatic chain containing the aceylenic linkage or linkages may be attached to an aromatic or alicyclic nucleus, such as 1-phenyl-butyne-2, or the like, its homologues or analogues. In all of these compounds which may be isomerized in accordance with the present invention, the aliphatic chain containingthe acetylenic linkage must contain at least four The alicarbon atoms, none of the acetylenic carbon atoms being attached to a tertiary carbon atom. In other words, the process covers the isomerization of hydrocarbons having the general for-.

(wherein the various Rs may be a hydrogen atom, or a saturatedor unsaturated alkyl, aryl or aralkyl radical), to produce hydrocarbons containing at least two olefinic linkages which are in conjugated relation with respect to each other. In case of hydrocarbons having the second of the above-outlined formulae, it is preferable to have hydrogen atoms in place of at least one of the Rs thereof.

- It; has been previously found that isopropyl acetylene may be converted to isoprene by subjecti'ng the'isopropyl acetylene, preferably under a reduced pressure, to an elevated temperature in the presence of a contact substance consisting of or containing alumina. This is disclosed in the U. S. Patent No. 1,083,165, which teaches that in good yields from acetylenic hydrocarbons the acetylenic carbons of which are not attached to any highly reactive tertiary carbon. Furthermore, the mere fact that the aforementioned patent teaches that the asymmetrical acetylene compound containing a highly reactive tertiary carbon atom attached directly to one of the acetylenic carbons, can be isomerized to a poly-- olefin, cannot be considered as even remotely suggesting that the relatively stable acetylenic hydrocarbons in which no acetylenic carbon is attached to a tertiarycarbon atom, and particularly the symmetrical acetylenic hydrocarbons of the above class, such as dimethyl acetylene and the like, or hydrocarbons which are readily convertible into symmetrical acetylenic hydrocarbons, such as ethyl acetylene, methyl propyl acetylene and the like, could be readily converted into the corresponding poly-olefins having the olefinic linkages in conjugated relation to each other. For instance, although isopropyl acetylene is highly reactive, dimethyl acetylene, by reason of its symmetrical structure, is extraordinarily stable and will remain unchanged in the absence of a catalyst even when heated to temperatures as high as 650 C. Therefore, it was heretofore unexpected that dimethyl acetylene or ethyl acetylene (which, as stated, is readily converted to dimethyl acetylene) could be readily and smoothly isomerized tobutadiene 'when subjected to elevated temperatures in the presence of the basic catalysts described hereinabove. Similarly, it could not be expected that the other hydrocarbons comprising or containingan acetylenic chain of at least four carbon atoms and in which none of the acetylenic carbons is attached directly to a tertiary carbon atom could be isomerized or rearranged to hydrocarbons having two or more double bonds in conjugated relation with respect to each other.

The isomerization or rearrangement according to the present process is effected by conveying the acetylenic hydrocarbon of the described class through a heated zone containing the basic catalyst. The operating temperature will vary depending on the acetylenic hydrocarbon subjected to rearrangement, residence time, pressure, use of diluents, etc. Generally, however, this temperature should be maintained below that at which excessive carbonization and/or rupturing of the carbon structure occurs. In the case of the rearrangement of dimethyl acetylene or of ethyl acetylene, the maximum temperature should be preferably maintained below about 500 C. As to the lower temperature limit, excessively low temperatures will decrease the rate of rearrangement. It may be stated, as a general rule, that temperatures above about 250 C., and preferably between about 350 C. and 400 0., should be employed especially when the rearrangement of dimethyl acetylene and/or ethyl acetylene (which are also frequently designated asbutyne-2 and butyne-l, respectively), or the like, is efi'ected in the presence of the described basic catalysts. However, as it will be obvious to those skilled in the art, higher or lower temperatures may be employed under different operating conditions and when other acetylenic hydrocarbons of the described class are rearranged to the corresponding poly-oleflns having conjugated double bonds.

According to oneembodiment of the invention the acetylenic hydrocarbon is conveyed at an.

optimum or desired rate through a reaction zone or tube containing the described catalyst heated to the optimum temperature. The eflluent gases are then treated by any one of the'known methods, such as condensation and/or fractional distillation, to separate the obtained poly-oleflns from the unreacted acetylenic hydrocarbons which may then be recycled through the reaction zone to eflect the rearrangement of further quantities thereof.

The following example is introduced. for the purpose of illustratingmodes of executing the process of the present invention and the results obtained thereby. It is to be understood, however, that the invention is not limited to the specific materials or conditions of operation disclosed.

Example An hydrocarbon fraction boiling between 8 and 40 C. and predominating in dimethyl acetylene and ethyl acetylene was conveyed through a Pyrex glass tube 50 centimeters long and 1.4 cm. in diameter. This tube was filled with commercial "Activated alumina and was enclosed in a metallic heating block which allowed a uniform heating of the tube. The hydrocarbon fraction was conveyed through the tube at a rate equivalent to about 0.7 cc. of liquid per minute, the temperature of the block being about 383 C., while that of the tube was slightly higher (408 C.) due to the slightly exothermic character of the rearrangement reaction. The eiiluent vapors were liquefied by cooling, and were analyzed by fractional distillation. It was thus found that the product contained about 11.7 weight percent of butadiene based on the hydrocarbon fraction introduced into the reaction tube. Actually, the yield was somewhat higher since about 12.3 weight percent of the feed was lost due to the inefiicient methods employed for the recovery, condensation and fractional distillation of the efliuent vapors.

By recycling the remaining 76% of the unchanged hydrocarbons, it was possible to increase considerably the ultimate yield of butadiene by the rearrangement of the dimethyl and ethyl acetylenes present in the treated hydrocarbon fraction.

Although the above test was effected at atmospheric pressures, the process may also be carried out at reduced or superatmospheric pressures. For instance, good yields of the poly-olefins, such as butadiene, may be obtained by efiecting the above-described rearrangement of the corresponding acetylenic hydrocarbons at a pressure of between about 20 and 40 millimeters of mercury. Obviously, the optimum operating temperature will change depending on the pressure employed. Instead of effecting the reaction under a vacuum, a dilution with a diluent, such as nitrogen, or the like, may be employed. The ratio of the diluent to the acetylenic hydrocarbon to be rearranged in accordance with the present invention may vary within wide limits.

The term activated alumina is used herein and in the appended claims to designate an aluminum oxide which is characterized by possessing the physical structure and surface characteristics of the "Activated alumina of commerce, which product is a well known and readily available article of commerce. It has been prepared and sold in this country since 1930, being recommended and used for adsorption of gases and vapors from gaseous mixtures. Activated alumina has been so named because of its active adsorption properties for gases and vapors, and not because of any catalyst activity. The fundamental diiference between an activated alumina and an ordinary alumina is that the former possesses active vapor adsorption characteristics which the latter does not. This material is termed activated alumina which is alumina alpha monohydrate prepared by partial dehydration of alpha alumina trihydrate precipitated from an aluminate solution.

As is well known to the art, an activated alumina having the physical structure and active adsorption properties (surface characteristics) of the "Activated alumina of commerce can be prepared in a variety of suitable manners. U. S. Patents 1,868,869 and 2,015,593 each describe a diflcrent method for the production of such an charge pipes used in the execution of the Fickes- Sherwin modification of the Bayer process. Activated alumina may also be prepared by precipitating aluminum hydroxide from an aqueous sodium aluminate solution by passing slowly thereinto a stream of gaseous CO2, and drying the resulting product by heating in air at about 600 C. Activated alumina can be prepared in still another manner which consists in treating aluminum amalgam under water and calcining the resulting fibrous aluminum hydroxide as described in K. A Hofmans, "Lehrbuch der Anorganischen Chemie," 6th edition, p. 483.

We claim as our invention:

1. A process for the production of butadiene which comprises heating a butyne to a temperature of between about 350 and 400 C. in the presence of an alumina which is alumina alpha monohydrate prepared by partial dehydration of alpha alumina trihydrate precipitated from an aluminate solution, and separating the butadiene from the unreacted acetylenic hydrocarbons.

2. A process for the production of butadiene which comprises heating a butyne to a temperature favoring the rearrangement of the acetylenic hydrocarbons to butadiene, but below the temperature at which substantial decomposition of the carbon structure occurs, in the presence of a catalyst comprising an alumina which is alumina alpha monohydrate prepared by partial dehydration of alpha alumina trihydrate precipitated from an aluminate solution. and separating the butadiene from the unreacted acetylenic hydrocarbons.

3. The process according to claim 2, wherein the rearrangement reaction is efiected at a pressure of between about 2'0 and 40 millimeters of mercury.

4. A process for the production of butadiene which comprises heating a butyne to an elevated temperature above 250C. but below that atwhich substantial decomposition of the carbon structure occurs, in the presence of a catalyst comprising alumina alpha monohydrate prepared by partial dehydration of alpha alumina trihydrate precipitated from an aluminate solution.

5. The process according to claim 4, wherein the rearrangement is effected at a temperature of between about 300 and 400 C.

6. A process for the manufacture of butadiene which comprises heating a butyne to a temperature of above 250 C:in the presence oi. a catalyst comprising alumina alpha monohydrate prepared by partial dehydration of alpha alumina trihydrate precipitated from an aluminate solution, and separating the butadiene from the unre acted acetylenic hydrocarbons.

7. In a process for effecting the rearrangement of an acetylenic hydrocarbon of at least four carbon atoms in which no acetylenic carbon is attached to a tertiary carbon atom, to a product containing the same number 01' carbon and hydrogen atoms but containing at leasttwo olefinic linkages in conjugated relation to each other, the step of contacting said acetylenic hydrocarbon, at an elevated temperature above 250 C. but below the temperature at which substantial decomposition of the carbon structure occurs, with a catalyst comprising alumina alpha monohydrate prepared by partial dehydration of alpha alumina trihydrate precipitated from an aluminate solution.

8. In a process for the manufacture of hydrocarbons containing at least two oleflnic linkages in conjugated positions with respect to each other, the step of heating an acetylenic hydrocarbon of at least four carbon atoms and'in which no acetylenic carbon is attached to a tertiary carbon atom at a. temperature of above 250 C., in the presence of a catalyst comprising alumina alpha monohydrate prepared by partial dehydration of alpha alumina trihydrate precipitated from an aluminate solution.

9. A process for the production of butadiene which comprises contacting a vaporcus hydrocarbon fraction predominating in butynes with a catalyst comprising alumina alpha monohydrate prepared by partial dehydration of alpha alumina trihydrate precipitated from an aluminate solution, at a temperature above 250 C., but below that at which substantial decomposition of the,

carbon structure occurs, and fractionally recovering the-butadiene formed from the unreacted hydrocarbons.

10. A process for the production of butadiene which comprises contacting a vaporcus hydrocarbon fraction predominating in butynes with alumina which is alumina alpha monohydrate prepared by partial dehydration of alpha alumina trihydrate precipitated from an aluminate solution, at a temperature or between about 300 C. and 400 C., for a period of time sufficient for efiecting the rearrangement, and separating butadiene from the unreacted hydrocarbons. 

